1. Field of the Invention
This invention relates to a composition of matter comprising a physical mixture of pyrogenic, hydrophobized silica and paraffin waxes. The invention also relates to the use of this physical mixture as a defoaming composition in dishwashing detergents and particularly in substantially surfactant-free, alkaline detergents used to machine wash objects having hard surfaces. The invention also relates to dishwashing detergents containing the physical mixture.
2. Description Of The Relevant Art
It is known to use commercially available, substantially surfactant-free, alkaline detergents to wash objects having hard surfaces, such as crockery, glasses and cutlery in standard commercially available dishwashing machines. It is also known to use such detergents to wash eggs from egg-laying batteries in the appropriate machines before mechanical hatching. It is also known to use such alkaline detergents for the removal of food and other dirt remains from the washing machines.
However, detergency is impaired by the formation of foam in the washing machines. The reasons for foam formation include:
the presence of foam-intensive food remains on crockery (for example egg, milk powder); PA1 a fall in temperature below the minimum operating temperatures which subsequently gives rise to foaming in heavy-duty machines because of entrained rinse-aid surfactants; PA1 unintentional emptying of the cleaning tank of heavy-duty washing machines accompanied by air being taken in by the recirculation pumps, which occurs, for example, when the machines are incorrectly loaded with articles having large surface areas, such as trays or the like, or when tank pipes are blocked by the remains of feathers, etc.; and PA1 faults in the design of the washing machine, such as poor zone separation in multiple-tank installations or inadequate liquor level. PA1 High specific activity, so that the amount of the defoaming agent in the detergent as a whole may be minimized; PA1 Chemical compatibility with other ingredients, particularly with caustic alkalis, alkalis, such as metasilicates, and chlorine carriers; PA1 No adverse effect upon shelf life; PA1 Ecological and toxicological acceptability; PA1 Good biodegradability; and PA1 An insignificant silicone content to avoid "siliconizing" the articles being washed. PA1 (a) from about 20 to 60% by weight of microcrystalline paraffin wax having a solidification point of from about 60.degree. to 95.degree. C., PA1 (b) from about 15 to 60% by weight of hard paraffin having a solidification point of from about 40.degree. to 60.degree. C., and PA1 (c) from about 1 to 50% by weight of soft paraffin having a solidification point of from about 32.degree. to 42.degree. C.
Accordingly, foaming in domestic or industrial washing machines gives rise to a reduction in detergency because the spraying pressure falls drastically, the water no longer reaches the articles to be washed, and the mechanics of the wash liquor lose significance as a detergent factor. As a result of inadequate detergency, the dry shine effect in the case of crockery, for example, may not be achieved and, in unfavorable cases, damage can be caused both to the articles being washed and to the washing machine.
Although solutions to the problem of foaming in washing machines have been available for some time, they have never been totally satisfactory. For example, silicone-containing emulsions are separately added to the washing tanks of heavy-duty washing machines. Although these silicone-containing emulsions bring about the immediate collapse of any foam present, they have to be kept available separately in addition to the detergent and the rinse aid and thus may be forgotten by the user.
In addition, when silicone-containing defoaming agents are used, either as a separate product or incorporated in the detergent or, as is generally the case, in the rinse aid, the articles being washed are always in danger of becoming "siliconized." This adversely affects the wettability of the surfaces of the articles and can give rise to problems both in domestic and in commercial kitchens. For example, in the case of new-laid eggs, "siliconizing" can result in blocking of the fine shell pores, so that the contents of the eggs fail to receive oxygen and die, producing a reduction in the hatching rate.
Even the use of highly propoxylated, foam-suppressing surfactants, such as the adduct of polyglycerine and 22 moles of propylene oxide, which adduct has a molecular weight of around 2,000, is not a practicable solution to the problem. These surfactants tend to interact with ingredients of the detergents, particularly with caustic alkalis and chlorine donors, to discolor the products. At the same time, the defoaming effect of the additives diminishes.
In view of these circumstances, defoaming agents for dishwashing detergents have to satisfy the following requirements: